Unchartered waters if deal rejected: May

British Prime Minister Theresa May has warned Tory MPs they face "uncharted waters" if they reject her Brexit deal.

With a looming Commons vote, May is fighting to save both her Brexit plan and her premiership in the face of a mounting Tory revolt.

Downing Street insisted that the vote would still go ahead on Tuesday amid speculation she might be forced to delay the showdown.

"It would mean grave uncertainty for the nation with a very real risk of no Brexit or leaving the European Union with no deal," May told the Mail on Sunday.

"We have a leader of the opposition who thinks of nothing but attempting to bring about a general election, no matter what the cost to the country.

"As someone who cares passionately about my country and my party, I believe Jeremy Corbyn getting his hands on power is a risk we cannot afford to take."

Reports suggested May could make an emergency trip to Brussels ahead of a planned summit on Thursday in an effort to secure further concessions in an effort to win over critics of her plan.

The prime minister's comments came as her government was hit by another resignation over the Brexit plan.

Will Quince, a ministerial aide to Defence Secretary Gavin Williamson, hit out at the backstop plan to avoid a hard border with Ireland, saying it could result in the UK being "tied to the negotiating table for years, until we agree to anything in desperation" to get out of the situation.

The same newspaper reported that another parliamentary private secretary was on the verge of quitting, and said Cabinet Brexiteer Penny Mordaunt was considering whether to back the deal or resign.

But May insisted her deal was the best way for Brexiteers to get the UK out of the European Union.

With the vote expected to result in a government defeat, some Cabinet ministers have urged her to delay while others have already begun promoting the idea of alternatives.

Work and Pensions Secretary Amber Rudd suggested a Norway-plus model, remaining in both the single market and customs union, as a "plausible" option that could get through the House of Commons.

But Brexiteers would loathe an arrangement that keeps the UK aligned to EU rules without a seat at the table in Brussels and does little, if anything, to tackle free movement.